In typical image encoding and decoding methods, in order to encode an image, one picture is split into macro blocks. After that, prediction encoding, is performed on each macro block by using inter prediction or intra prediction.
Inter prediction refers to a method of compressing an image by removing temporal redundancy between pictures and its representative example is motion estimation encoding. In motion estimation encoding, each block of a current picture is predicted by using at least one reference picture. A reference block that is most similar to a current block is found within a predetermined search range by using a predetermined evaluation function.
A current block is predicted based on a reference block, and a residual block obtained by subtracting from the current block a prediction block generated as a prediction result is encoded. In this case, in order to more accurately perform prediction, interpolation is performed on a range of searching the reference picture, sub-pel-unit pixels smaller than integer-pel-unit pixels are generated, and inter prediction is performed on the generated sub-pel-unit pixels.